This application is in response to RFA-HL-08-007 "Targeted Approaches to Weight Control for Young Adults". As outlined in the RFA, this application will focus on development, refinement, and evaluation of a behavioral approach to weight control in young adults, with the focus of this application being on enhancing long-term weight loss. Consistent with the RFA, young adults for this application are defined as individuals 18-35 years of age. The prevalence of obesity in young adults has been increasing, and excessive body weight have been linked to numerous chronic conditions including cardiovascular disease, diabetes, many forms of cancer, and numerous musculoskeletal problems. The focus of this application is to develop and evaluate interventions that may be appropriate for young adults to improve weight loss outcomes following a 24 month intervention. Therefore, the primary aim of this study is to examine whether an enhanced weight loss intervention (EWLI) that includes technology components results in improved weight loss in young adults (18-35 years of age) compared to a standard behavioral weight loss intervention (SBWP) over a period of 24 months. Additional aims include examination of these interventions on changes in body composition, body fat distribution, fitness, physical activity, dietary intake, and behavioral/psychosocial measures that may be predictive of behavior change. Assessments will occur at 0, 6, 12,18, and 24 months. This study involves the recruitment of 480 overweight and obese young adults (18-35 years of age). Subjects will participate in a 24 month behavioral weight loss program that includes a reduction in energy ntake and moderate-to-vigorous intensity exercise (progressively increasing from 100 to 300 minutes per week). Subjects will be randomized to receive this intervention (SBWP) or this intervention in combination with technology enhancements (EWLI). EWLI will receive daily text messaging prompts to reinforce adherence to the behavioral intervention from months 7-24, and will wear a monitor from months 13-24 that provides real-time feedback on energy expenditure and achievement of daily physical activity goals. It is hypothesized that these technology enhancements to EWLI will significantly improve weight loss, body composition, body fat distribution, fitness, physical activity, and dietary intake compared to SBWP. RELEVANCE (See instructions): Obesity rates of young adults have significantly increased and the ability to sustain weight loss long-term in this age group has been less than desirable. Therefore, there is a need to develop and implement effective intervention initiatives to address this public health concern, which is the focus of this proposed intervention study. (End of Abstract)